1. Field of the Invention:
The present invention generally relates to railroad interlocking controls for regulating flow of traffic through an interlocking track layout. More particularly, the invention relates to such a control utilizing a plurality of programmable controllers arranged to share operative control of switch and signal devices in a bottleneck area.
2. Description of the Prior Art:
In a track layout having a number of switch turnouts and rail crossings, it is necessary to assure a clear route for an entering train in order to fully exploit the train's speed capabilities. The concept of railroad interlocking, developed as early as 1857, provides this clear route assurance by preventing other vehicles from taking routes conflicting with that of the entering train.
One common interlocking system is referred to as route interlocking. In this system, a dispatcher or other operator chooses a route by pushing respective entrance and exit buttons on a control console having a diagram of the track layout. The interlocking control system then automatically locates the most efficient route between the selected entrance and exit points. The system further sets up all track switches along the route and clears an entrance signal. Typically, the wayside signals through the route indicate to the train engineer the allowed maximum speed in a particular track section. An additional feature, known as sectional route locking, releases sections of the route after the train has passed so that other routes may be set up. A typical prior art route interlocking system incorporating many of the above features is fully described and shown in U.S. Pat. No. 4,066,288, issued to J. Calvin Elder on Jan. 3, 1978. This patent is incorporated herein by reference.
Original interlocking systems were completely mechanical. Eventually, however, these mechanical systems were replaced by electrical systems utilizing vital relays to control electrically actuated switch and signal devices. In order to decrease both switching time and cost, recent advances in technology had made it desirable to replace these vital relays with electronic circuits. The first electronic systems used discrete solid state components. Eventually, however, discrete components were replaced by integrated circuits. For greatest flexibility, the most modern controllers are microprocessor-based and can be programmed using software or firmware for use with virtually any interlocking arrangement. Controllers of this type have been marketed by Union Switch and Signal, Inc of Pittsburgh, Pa. under the trademarks MICROLOCK and GENISYS.
In normal operation where multiple programmable controllers are used to control large interlockings, they are typically either linked serially or the interlocking is split up so that particular units handle specific functions. If any one of the units fail, information to move traffic through a bottleneck could be inhibited. In this situation, redundancy has been important. Normally, each unit is changed to a normal/standby configuration which can become costly. Also, the fail-over logic may be cumbersome.